The investigation proposed will elucidate several properties of the tooth-saliva interface which are relevant to the etiology of root caries. Of particular interest are those biochemical and microbiological factors that determine the colonization of root surfaces by oral bacteria. The colonization of teeth by microorganisms involves their attachment to the acquired pellicle. Although limited knowledge of this integument is available in the case of enamel, virtually no information is available in the case of root surfaces. Thus, it is proposed to determine and characterize the components of the pellicle overlying root surfaces. This will be accomplished through direct examination of natural pellicles using various chromatographic and immunochemical techniques. In addition, adsorption of specific salivary macromolecules onto dentin and cementum will be investigated and the results compared with those obtained with dental enamel as an adsorbent. It is also proposed to investigate possible differences in the selectivity of bacterial attachment to human enamel and root surfaces in vivo. For this purpose, mixtures of pertinent streptomycin-resistant bacteria (A. viscosuus, A. naeslundii, S. sanguis, and S. mutans) will be introduced into the oral cavity of subjects and the ratios of attached microorganisms on the crowns and on the exposed root surfaces will be determined. Comparison of these ratios will yield information about possible differences in the adsorption of microorganisms onto the two kinds of surfaces. The third aspect of the present project concerns the investigation of specific salivary constituents that may serve as acceptors for bacterial attachment to the acquired pellicle. This will involve the isolation and purification of salivary macromolecules that will be used as adsorbates in experiments in which prominent oral microorganisms will be the adsorbents. It is proposed to obtain isotherms for the adsorption of each salivary macromolecule to the bacteria, so that the number of attachment sites and the affinituy constants can be derived. Significant interactions between specific salivary protens and oral bacteria will therefore be revealed.